Method of designing an integrated circuit memory architecture

ABSTRACT

A method for generating a memory of various sizes and configurations uses a plurality of banks. The banks are selected to meet memory requirements and size constraints and are arranged in an orthogonal array. Critical paths are minimized using commercially available software.

FIELD OF THE INVENTION

The invention relates generally to the design of memories and morespecifically to the computer-based design of memories of various sizeand configurations.

BACKGROUND OF THE INVENTION

With today's sub-micron CMOS technology, it is possible to put millionsof transistors on a single chip. This has made the realization ofsystems on a chip (SOC) possible, but has also significantly increasedthe complexity of VLSI design. Design automation has become veryimportant to efficiently manage SOC realizations. As most SOCs needvarious types of memories, the need for generator- (or compiler-) basedmemories is rapidly growing to reduce time to market, development costand improve reliability.

Many SOCs also require large memories, often in the mega-bit range.Providers of application specific integrated circuit (ASIC) memorylibraries are trying to address such mega-bit memory requirements byextending the upper capacity limit of their basic memory offerings.Usually, this approach suffers adversely in area, performance and powerconsumption. In general, merely scaling up an existing small capacitymemory generator (e.g., 64 Kbit ROM) to a large capacity memorygenerator (e.g., 2 Mbit ROM) adversely affects memory performance.

More specifically, conventional approaches to generating a largecapacity memory include interconnecting a plurality of complete memoryblocks using software routing tools. In this approach, common signals(i.e. clock, address, data, etc.) are heavily loaded. This results insignal skews, upsets timing constraints and increases access time.Moreover, the software routing tools typically do not lead to regular,evenly spaced, routing. This causes differences in the timingcharacteristics in the different memory blocks. Minimizing suchdifferences is a tedious iterative process which may or may not producegood results. In addition, such methods provide little flexibility interms of layout configuration.

Accordingly, a memory generator is desired which provides goodscaleability with a variety of configurations. The memory generatorshould operate to minimize area, maximize speed and minimize powerconsumption. Moreover, a memory generator which produces one functionalmodel, and thus one timing model to fully characterize the memory ispreferred to simplify design considerations.

SUMMARY OF THE INVENTION

In one preferred embodiment, a method of designing a memory for a systemon a chip application begins with a required memory capacity anddeterminable physical boundaries. The method selects a plurality ofmemory banks wherein each bank has a height, a width and a memorycapacity. The method tiles the plurality of memory banks. Adjacent bankshave matching dimensions along a common boundary and address signals arerouted between adjacent banks. The method designs control circuitry tooperationally couple with the plurality of memory banks. The controlcircuitry is configured to generate addressing signals for selectingaddress locations from within the plurality of memory banks.

In another preferred embodiment, a memory for an SOC applicationincludes a plurality of memory banks configured in an array of at leastone column and at least one row. Each of the plurality of memory bankshas a plurality of memory locations. The memory includes a row decoderoperationally coupled with the plurality of memory banks. The memoryalso includes a column decoder operationally coupled with the pluralityof memory banks. The row decoder and column decoder are configured toselect respective ones of the plurality of memory banks.

In yet another preferred embodiment of the invention, a memory for usewith a system on a chip includes a plurality of banks arrayed into aplurality of rows and a plurality of columns. Each bank has a pluralityof memory locations. The memory includes a bank row decoderoperationally coupled with the plurality of banks. The memory includes abank column decoder operationally coupled with the plurality of banks.The bank row decoder and bank column decoder are configured to select arespective one of the plurality of banks. The memory also includes aplurality of address row decoders each operationally coupled with arespective one of the plurality of rows. Finally, the memory includes aplurality of address column decoders each operationally coupled with arespective one of the plurality of columns. The address row decoders andaddress column decoders are configured to select respective ones of theplurality of memory locations in one of the plurality of banks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one preferred embodiment of a memory havinga plurality of banks.

FIG. 2 is a flow chart showing the process of reading data from a memorylocation within the memory of FIG. 1.

FIG. 3 is a block diagram of the memory of FIG. 1, showing the aspectrelationships between the plurality of banks.

FIG. 4 is a block diagram of another preferred embodiment of a memoryhaving a plurality of banks showing the aspect relationships between theplurality of banks.

FIG. 5 is a circuit diagram of the critical paths of the memory of FIG.1.

FIG. 6 is a partial circuit diagram of the memory and control circuitryfor a bank generated using Technology Independent DevelopmentEnvironment (TIDE) software produced by Mentor Graphics.

FIG. 7 is a timing diagram showing the relationships between selectedsignals in the circuit of FIG. 5.

FIG. 8 is a flow chart showing one preferred process for designing amemory using a plurality of banks.

DETAILED DESCRIPTION

Turning to FIG. 1, one preferred embodiment of a memory having aplurality of banks is described. The memory is made up of severalsub-blocks or memory banks 111, 121, 131, 141, 151, 161, 171, 181 and191. Each bank includes a plurality of memory locations and relatedcontrol circuitry, however, the individual banks do not include enoughcontrol circuitry to operate as a stand-alone memory. Instead, the banksare interconnected (or tiled) to form a larger memory. Additionalcontrol circuitry is provided to operate the memory. The controlcircuitry includes a bank row decoder 101, a bank column decoder 105,row decoders 102, 103 and 104, and column decoders 106, 107 and 108.

More specifically, bank 111 includes a memory bit cell 110, a sourceaddress selector 112, an output buffer 116 and bank control circuitry114. Similarly, bank 121 includes a memory bit cell 120, a sourceaddress selector 122, an output buffer 126 and bank control circuitry124; bank 131 includes a memory bit cell 130, a source address selector132, an output buffer 136 and bank control circuitry 134; bank 141includes a memory bit cell 140, a source address selector 142, an outputbuffer 146 and bank control circuitry 144; bank 151 includes a memorybit cell 150, a source address selector 152, an output buffer 156 andbank control circuitry 154; bank 161 includes a memory bit cell 160, asource address selector 162, an output buffer 166 and bank controlcircuitry 164; bank 17 1 includes a memory bit cell 170, a sourceaddress selector 172, an output buffer 176 and bank control circuitry174; bank 181 includes a memory bit cell 180, a source address selector182, an output buffer 186 and bank control circuitry 184; and bank 191includes a memory bit cell 190, a source address selector 192, an outputbuffer 196 and bank control circuitry 194.

As shown, the banks are orthogonally arrayed to form three columns andthree rows. Banks 111, 121 and 131 form a first row. Banks 141, 151 and161 form a second row. Banks 171, 181 and 191 form a third row.Similarly, banks 111, 141 and 171 form a first column, banks 121, 151and 181 form a second column, and banks 131, 161 and 191 form a thirdcolumn.

Bank row decoder 101 connects to each of the banks. More specifically,bank row decoder 101 connects to the source address selector and bankcontrol circuitry for each of the banks. These connections are used toselect a memory bank and to enable its output. Similarly, bank columndecoder 105 connects to the source address selector and bank controlcircuitry for each of the banks.

Each bank includes a plurality of memory locations. These memorylocations may be selected by specifying an address row and addresscolumn within a particular bank. The address row and address columnsignals are provided by an address row decoder and an address columndecoder. As shown, address row decoder 102 connects to the sourceaddress selector for each bank in the first row (i.e., address rowdecoder 102 connects to source address selectors 112, 122 and 132).Similarly, address row decoder 103 connects to the source addressselector for each bank in the second row, and address row decoder 104connects to the source address selector for each bank in the third row.

The address column decoder 106 connects to bank control circuitry foreach bank in the first column (i.e., bank control circuitry 114, 144 and174). Similarly, the address column decoder 107 connects to bank controlcircuitry for each bank in the second column (i.e., bank controlcircuitry 124, 154 and 184) and address column decoder 108 connects tobank control circuitry for each bank in the third column (i.e., bankcontrol circuitry 134, 164 and 194).

To select a particular address location within the memory, an addressbus 100 is connected to the bank row decoder 101, bank column decoder105, address row decoders 102, 103 and 104, and address column decoders106, 107 and 108. Based upon signals received from the address bus 100,the bank row decoder 101 generates a signal for selecting a bank row andthe bank column decoder 105 generates a signal for selecting a bankcolumn. Similarly, the address row decoders 102, 103 and 104 generate asignal for selecting an addressed row within a bank and the addressedcolumn decoders 106, 107 and 108 generate a signal for selecting anaddressed column within a bank.

Together, bank row decoder 101, bank column decoder 105, address rowdecoders 102, 103 and 104, and address column decoders 106, 107 and 108operate to select one address location within the memory. During a readoperation, data from the selected address location is provided over itsrespective data bus 109 a, 109 b, 109 c.

The process for reading data from a memory location will now bedescribed in further detail with reference to FIG. 2. At block 210, theprocess begins upon receiving a memory address over the address bus 100(FIG. 1). These address signals are provided to bank row decoder 101,bank column decoder 105, address row decoders 102, 103 and 104, andaddress column decoders 106, 107 and 108.

For purposes of illustration, a memory address within bank 161 isselected. Accordingly at block 212, the bank row decoder 101 generates asignal operative to select row two and the bank column decoder 105generates a signal operative to select column three. The address rowdecoder 103 and the address column decoder 108 generate signalsoperative to select an address location within bank 161.

The signals from bank row decoder 101, bank column decoder 105 andaddress row decoder 103 are provided to source address selector 162.Together, the signal lines conveying these signals are called a “localword line.” The local word line selects a row of memory addresses withinone bank. By gating the signals from bank row decoder 101 and bankcolumn decoder 105, only one local word line will be generated. In thisexample, the local word line selects a row of memory addresses withinbank 161. Of course, the contents of an entire row of memory addresseswithin the selected bank 161 cannot be provided simultaneously over thedata bus 109 c.

Accordingly at block 214, the signals from the bank row decoder 101, thebank column decoder 105, and the address column decoder 108 are providedto bank control circuitry 164. Since the address row decoder 103 hasalready selected a row of addresses within bank 161, bank controlcircuitry 164 uses the signal from the address column decoder 108 toselect one address location from within such row of bank 161.

At block 216, the contents from the selected memory location areprovided to output data buffer 166. Data buffer 166 is multiplexed withthe other data buffers 136, 196 onto their data bus 109 c so that onlyone bank provides data to the data bus 109 c at a time. In a typicalapplication, the data bus 109 c connects to other components of an SOC.

In designing a memory for an SOC application, a particular memory sizeis often desired. In addition, depending upon the circuit layout, theapplication may require specific dimensions to minimize wasted space ona silicon wafer. For example an application may require a 1 Mb memoryhaving a substantially square shape, alternatively an application mayrequire a 1 Mb having a substantially rectangular shape with aparticular ratio between the length and width. To meet the demands of aparticular application, a plurality of banks are selected andinterconnected to form a complete memory. The banks are selected toprovide a sufficient number of memory locations and to meet any sizeconstraints.

Turning to FIG. 3, the aspect ratios between the banks of FIG. 1 will bedescribed. As shown, bank 141, bank 151, bank 171 and bank 181 are eachof type A. The type A bank provides 64 Kb of memory. As mentioned above,the memory locations within the bank are partitioned by row and column.The type A bank provides 256 rows and 256 columns of memory locations.Banks 111 and 121 adjoin bank 141 and bank 151, respectively. Banks 111and 121 are each of type B. The type B bank provides 32 Kb of memory.The type B bank provides 128 rows and 256 columns of memory locations.Banks 161 and 191 are each of type C. The type C bank also provides 32Kbof memory. Unlike a type B bank, however, a type C bank provides 256rows and 128 columns of memory locations. Finally, bank 131 is of typeD. The type D bank provides 16 Kb of memory. The type D bank provides128 rows and 128 columns of memory locations. Together banks 111, 121,131, 141, 151, 161, 171, 181 and 191 provide 400 Kb of memory.

As may be noted from the forgoing description, the vertical dimension ofeach block matches that of adjoining blocks. More specifically, thenumber of rows in block 111 matches that of block 121; likewise thenumber of rows in block 121 matches that of block three 131. In otherwords, the vertical dimension is the same throughout a row.

Similarly, the horizontal dimension of each block matches that ofadjoining blocks. More specifically, the number of columns in block 111matches that of block 141; likewise the number of columns in block 141matches that of block 171. In other words, the horizontal dimension isthe same throughout a column.

Although the memory shown in FIG. 3 includes three columns and threerows of memory blocks, the number of columns and rows and theirrespective dimensions may be varied according to the requirements of anSOC. Turning to FIG. 4, another memory having multiple blocks andassociated addressing hardware is described.

Banks 410-414 and 420-424 are each of type A. Banks 416 and 426 are oftype E. A type E bank provides 16 Kb of memory. The type E bank provides256 rows and 64 columns. The memory also includes a bank row decoder(“BRD”) 452 and a bank column decoder (“BCD”) 454, as well as addressrow decoders (“ARD”) 448 and 450, and address column decoders (“ACD”)434, 436, 438, 440, 442 and 444. These blocks provide the samefunctionality as those of FIG. 1.

As with the memory of FIG. 3, the vertical dimensions are the samethroughout a row and the horizontal dimensions are the same throughout acolumn of memory blocks. By matching the horizontal and verticaldimensions of adjacent memory blocks, the address and data signals maybe easily routed from one bank to the next. Turning back to FIG. 1, thesignals from bank row decoder 101, and address row decoders 102, 103 and104 are simply passed between adjacent banks along a row of memorybanks. Similarly, the signals from bank column decoder 105 and addresscolumn decoders 106, 107 and 108 are simply passed between adjacentbanks along a column of memory banks. Other signals, such as a clock,may be easily provided by passing the signal along each of the rows oreach of the columns of memory banks.

One important advantage of the above described design involves theability to determine accurately the memory characteristics, includingtiming characteristics. As described above, many conventional techniquesinvolve scaling an existing memory to meet a particular set of designrequirements. Conversely, the subject invention selects from a set ofpredefined memory banks, each of which have well-known characteristics.Moreover, the tiling of these banks produces a memory array which may becharacterized easily based upon the well-known characteristics of theindividual memory banks. More specifically, the dimension of a memoryarray may be easily determined by adding the dimensions of theindividual memory banks and associated control circuitry. Similarly, thetiming characteristics of the memory array may be determined easilybased upon the timing characteristics of the individual memory banks andassociated control circuitry. Thus, a memory array designed according tothe present invention avoids many of the time consuming and difficultiterative procedures commonly associated with scaling memories.

Turning to FIG. 5, the critical path of a 2 MBit ROM is described. Thecritical path defines the path of greatest delay, and is used todetermine timing constraints. The ROM includes 32 memory banksconfigured in 2 rows and 16 columns. Each bank provides 64 Kb of memoryso that the memory has a total of 2 Mb. An address within the space maybe selected using address lines 510 which provide 21-bit addressing. Oneof the address lines 510 is connected to the bank row decoder 522 via abank row decoder bus 512. Four of the address lines 510 are connected tocolumn decoder 528 over column decoder bus 520.

The bank row decoder 522 receives address signals from the bank rowdecoder bus 512 and generates row selection signals. When the bank rowdecoder bus 512 is in a first state, the bank row decoder 522 selects afirst row and when the bank row decoder bus 512 is in a second state,the bank row decoder 522 selects a second row.

Similarly, the bank column decoder 528 receives address signals from thebank column decoder bus 520 and generates column selection signals. Asthe bank column decoder bus 520 provides four lines, the bank columndecoder bus 520 may select between 16 columns. The address row decoder524 receives address signals from the address row decoder bus 516.Likewise the address column decoder 526 receives address signals fromthe address column decoder bus 518. Both the address row decoder bus 516and the address column decoder bus 518 provide eight lines. Accordingly,the address row decoder 524 and the address column decoder 526 mayselect between 256 rows and columns, respectively.

Signals from the bank row decoder 522, the bank column decoder 528 andthe address row decoder 524 are provided to the source address selector530. Preferably, the source address selector is implemented using an ANDgate or similar circuitry that provides such functionality. In response,the source address selector 530 generates a signal on the local wordline 531 which is used to select a row of addresses in memory bank 532.Since bank 532 is selected from a predefined set of memory banks, itstiming characteristics should be well defined.

Control circuitry 536 receives signals from the bank row decoder 522,the bank column decoder 528 and the address column decoder 526. Inresponse, control circuitry 536 generates a control signal for selectinga particular memory location. This signal is provided to output buffer534. Output buffer 534 provides the contents of the desired addresslocation to multiplexor 538. Multiplexor 538 selects an input based upona signal from the address column decoder 526 and provides that input tothe data bus 540.

For purposes of determining the critical path, loads consist of both thetransistor delays and interconnect delays. These delays are determinedusing π-modeling. Once the critical paths have been determined, variousdesign parameters may be adjusted to minimize memory access time.

For a memory bank having significantly more columns than rows, thecritical path for addressing a memory bank is from address bus 510,through bank column decoder 528, through source address selector 530 andthrough local word line 531. Hence optimization is performed on thispath.

For a memory bank having significantly more rows than columns, thecritical path for addressing a memory bank is from address bus 510,through bank row decoder 522, through source address selector 530 andthrough local word line 531. Hence optimization is performed on thispath.

The critical path from a memory bank 532 to the data bus 540 consists ofthe control circuitry 536, the output buffer 534 and the multiplexor538. Hence, optimization also is performed on this path.

In one preferred embodiment of the invention, commercially availablesoftware is used to design memory banks and related control circuitry.More specifically, Memory Builder software available from MentorGraphics Corp., 8005 S.W. Boeckman Road, Wilsonville, Oreg. 97070 may beused. The memory banks are designed for implementation on a 0.25 micronprocess. Of course, other software and/or other processes may also beused.

A critical portion of a preferred bank control circuit is detailed inthe circuit diagram shown in FIG. 6. This circuit was designed using theabove-mentioned software from Mentor Graphics. As will be explained infurther detail, a self-timed circuit, cross-coupled inverters as theload in the source amplifier, precharged dynamic decoding and shared bitlines are the key features used to minimize area and reduce access timeand power.

As shown, a self-timing scheme is implemented using a dummy column 602and dummy row 604. An actual row is used as the dummy row 604 becausedifferent rows have different loads depending on the number of 1's and0's programmed in each row. Self timer is activated at every read cycleafter the address is applied and a word line is selected. Self timerincludes dummy column 602, dummy row 604, dummy column discharge andcolumn loads. The self timer triggers the sense amplifier 610,deactivates the word line and starts the precharge circuit 612. Selftimer is carefully designed to ensure minimal access time for memoryblocks ranging from the smallest to the largest size. This isaccomplished by performing critical path simulations for all possiblememory size and configurations.

Sense amplifier 610 is implemented using a differential pair 611 anduses cross-coupled inverters as a sense amplifier load 614. Thedifferential pair 611 is enabled by an output signal (Sense-Enable) fromself timer 606. The reference voltage used for sense amplifier 610 isdesigned to drop at half the rate as the voltage on the bit line 616 toensure that the input to sense amplifier 610 quickly exceeds thethreshold voltage for reading both 0's and 1's. This threshold voltageis 250 mv. The bit lines of the adjacent bit cells 618 are shared tominimize area. The reference voltage drop is self terminated when thereference voltage falls below Vdd−Vtn to ensure sufficient voltage toeffectively trigger the sense amplifier 610. Vdd is the power supplyvoltage. Vtn is the threshold voltage of n-channel transistor. Theoutput of the sense amplifier 610 is usually latched. So, the latcheddata is read when output buffer 620 is enabled. To ensure that only onebank drives the bus, the output of the output buffer is multiplexed withthe other banks. The signals from the bank column decoder are used tocontrol the multiplexor. This ensures that only one bank column may putdata on a data bus 109 (shown in FIG. 1).

The critical path of the individual ROM bank shown in FIG. 6, wasoptimized by ensuring that the READY signal 622, which is controlled byself timer 606 occurs at the right time. The self timer 606 consists ofthe actual row selected and the dummy column 602. The READY signal 622is generated when the dummy column 602 is fully discharged. The dummycolumn discharge path is enabled by a dummy column discharge signalwhich is activated for each selected bit line. The READY signal 622, inturn, is used to control signals on local word line 531 (shown in FIG.5), column precharge 624 and sense-enable.

If READY signal 622 is generated too soon, then sense amplifier 610 willnot have received data from the selected bit cell. If it occurs toolate, the overall access time of the ROM will be unnecessarily delayed.Optimization of the READY signal 622 is done by manipulating thetransistor sizes of the self-timer circuitry.

Once the generation of the READY signal 622 is optimized, the relativefall times of local word line 531 (shown in FIG. 5) and column precharge624 must be adjusted since they are both generated by the READY signal622. Local word line 531 must be turned off before the is columnprecharged, so it may be necessary to delay the signal on columnprecharge 624 with buffers. For the simulations run on the 2 Mb ROMshown in FIG. 6, it was necessary to delay the column precharge signalwith several buffers.

Worst case timing simulations were run on the above-described circuit.The simulations were performed using slow-slow, 2.2v, 110 degreesCelsius, and 1pf output loads as the circuit parameters. The results areshown in the timing diagram of FIG. 7. In particular, the clock, columnprecharge, local word line, sense enable, and data out signals areshown. The total access time is 10 ns. This time includes 4 ns for theactivation of local word lines, 3 ns to enable the sense amplifier, and3 ns for signal propagation from the sense amplifier to the final databus.

The process for designing a memory using the above-described banks willnow be described with reference to FIG. 8. At block 810, a designerdetermines the memory requirements of the particular application. Thememory requirements include determining the bit requirements of theapplication, as well as any physical size constraints. At block 812, thedesigner selects from a number of memory banks to meet the designrequirements. For example, the banks shown in FIG. 3 could be selectedwhere a 400 kb memory is needed.

At block 814, the memory blocks are tiled in an orthogonal array. Rowand column decode lines are arranged as shown in FIG. 1 so that they maybe shared among adjacent memory banks.

At block 816, appropriate address decoders are designed to provide therow and column decode signals. These decoders may be designed usingMentor Graphics TIDE or other commercially available memory generatorsoftware. The decoders are optimized so as to minimize delays along anycritical paths.

The above-described tiling of different memory banks provides highlyregular routing. Thus, a complete memory array can be characterizedusing this critical path analysis. Moreover, this approach requires lessarea since the row and column decode signals are shared among the memorybanks. This also reduces routing area. Because of the use of a regularstructure for tiling, the routing overhead is further minimized whichalso reduces area requirements. Smaller area reduces interconnects andcan improve the speed. With this tiling approach, the routing is highlyregular and thus one timing model and one functional model will sufficeto fully characterize the memory array.

Although the embodiments described herein are with reference to memorybanks having specific sizes, the present invention may be implementedusing a variety of memory banks of any given size. In addition, althoughthe embodiments described herein show specific circuit configurationsother designs may perform the same functionality or obtain the sameadvantages using different configurations. Those having ordinary skillin the art will certainly understand from the embodiments disclosedherein that many modifications are possible without departing form theteachings hereof. All such modifications are intended to be encompassedwithin the following claims.

We claim:
 1. A method of designing an integrated circuit memoryarchitect wherein the memory architecture has a required memory capacityand determinable physical boundaries, the method comprising: defining aset of individual memory bank designs such that each individual memorybank design has a set of characteristics that is different than the setof characteristics of other individual memory bank designs; tilingselected individual memory bank designs to provide a memory arrayarchitecture comprising rows and columns of memory banks such thatadjacent memory banks in the memory array architecture have matchingdimensions along a common boundary and wherein address signals arerouted between adjacent memory banks; and designing control circuitry tooperationally couple with the memory banks, wherein the controlcircuitry is configured to generate addressing signals for selectingaddress locations from within the memory banks.
 2. The method of claim 1and wherein each of the set of characteristics of each individual memorybank designs includes a memory cell matrix design that includes a numberof rows of individual memory cells and a number of columns of individualmemory cells, the rows and columns of individual memory cells beingorthogonally disposed, and wherein at least one of the number of rowsand the number of columns of a memory cell matrix design is differentthan at least one of the number of rows and the number of columns ofother memory cell matrix designs, and wherein the step of tilingcomprises: selecting individual memory bank designs such that eachmemory cell matrix design included in a row of the memory arrayarchitecture has the same number of rows of individual memory cells andsuch that each memory cell design included in a column of the memoryarray architecture has the same number of columns of individual memorycells.
 3. The method of claim 2, and wherein the step of tiling furthercomprises selecting the individual memory bank designs such that a sumof the memory capacities of the individual memory bank designs exceedsthe required memory capacity.
 4. The method of claim 3, and wherein thestep of tiling further comprises selecting the individual memory bankdesigns such that a sum of adjacent memory bank heights is less than aheight of the determined physical boundary and the sum of the adjacentmemory bank widths is less than a width of the determined physicalboundary.
 5. The method of claim 1, and wherein, in the step of tiling,row addressing signals are routed along common vertical boundaries ofmemory banks and column addressing signals are routed along commonhorizontal boundaries of memory banks.
 6. The method of claim 1, andwherein, in the step of designing control circuitry, the addressingsignals are configured to generate bank row and bank column selectsignals, wherein the bank row and bank column select signals identifyrespective ones of the memory banks.
 7. The method of claim 6, andwherein, in the step of designing control circuitry, the addressingsignals are further configured to generate address row and addresscolumn select signals, wherein the address row and address column selectsignals identify respective address locations within a selected memorybank.